I put several cauldrons around my base so they fill up when it rains and comparators next to it, to send a pulse to 2 command blocks. The first says "It's raining", and then the second replaces the filled cauldron with an empty cauldron, so it actually resets the machine. My idea was to have a funny mechanism to be able to know when it rains (by having a lot of cauldrons), but I saw they fill up and all comparators have no signal of it. But if I place a comparator on any other side of the cauldron it actually send a redstone signal. I also placed string over all comparators, and when they are off, I walked over the string and since it updated the comparator below, it suddenly send a redstone signal. So clearly there is a bug where when a cauldron fills up (at any high) by rain, it doesn't look around to see if any comparator around needs an update, thus making any machine related to detecting when a cauldron gets filled up by rain useless at this point. Thank you very much for your attention and have a nice day.